1. Field of the Invention
This invention relates in general to a spindle motors for disk drives, and more particularly to a mounting interface for a spindle motor.
2. Description of Related Art
Disk drive data storage devices are a popular medium for storing digital data. Disk drive data storage devices typically include at least one rotating disk, wherein digital data are written to and read from a thin layer of magnetizable material on the surface of the rotating disks. Write and read operations are performed through a transducer which is carried in a slider body. The slider and transducer are sometimes collectively referred to as a head, and typically a single head is associated with each disk surface. The heads are selectively moved under the control of electronic circuitry to any one of a plurality of circular, concentric data tracks on the disk surface by an actuator device. Each slider body includes a self-acting hydrodynamic air bearing surface. As the disk rotates, the disk drags air beneath the air bearing surface, which develops a lifting force that causes the slider to lift and fly several micro-inches above the disk surface.
In the current generation of disk drive products, the most commonly used type of actuator is a rotary moving coil actuator. The disks themselves are typically mounted in a “stack” on the hub structure of a brushless DC spindle motor. The rotational speed of the spindle motor is precisely controlled by motor drive circuitry which controls both the timing and the power of commutation signals directed to the stator windings of the motor.
More recently, personal computers have become more popular and are commonly located within the work space of the system user. This has prompted an increase in awareness of acoustic noise generated by the disk drives located within the personal computers. In certain markets, the amount of acoustic noise allowable in the work place is closely regulated. Accordingly, it has become common for system manufacturers to impose a “noise budget” on manufacturers of major system components, such as disk drives, which limits the amount of acoustic noise that such components can contribute to the overall noise of the system.
One of the principal sources of noise in disk drive data storage devices is the spindle motor which drives the disks at a constant speed. Typical spindle motor speeds have been in the range of 3600 RPM. Current technology has increased spindle motor speeds to 4800 RPM, 7200 RPM and above. Analysis of various types of disk drives has brought to light several different modes of acoustic noise generation which are attributable to the spindle motor and its control logic.
One mode of noise generation is sympathetic vibration of the disk drive housing in response to the rotating mass of the spindle motor. Another mode of acoustic noise generation is electromagnetic disturbances caused by the excitation of the stator mass by the application and removal of the commutation pulses that are used to drive the motor and control its speed. The commutation pulses are time, polarization-selected DC current pulses which are directed to sequentially selected stator windings. The rapid rise and fall times of these pulses act as a striking force and set up sympathetic vibrations in the stator structure.
Prior art attempts to reduce or eliminate noise include controlling the resonant frequency and damping vibrations. For example, in U.S. Pat. No. 5,376,850, acoustic noise is reduced by uncoupling the stator from hard contact with the stationary portion of the shaft. A plurality of O-rings interposed radially between the stator and the shaft of the spindle motor. Also, a non-metallic washer is positioned at one end of the shaft and an axial O-ring is positioned at the other end of the shaft.
Other attempts have been directed at shifting resonant frequencies. For example, in U.S. Pat. No. 5,625,511, the spindle motor shaft is formed with stepped surfaces to reduce disk drive acoustic noise by tuning the torsional frequency of the spindle motor shaft away from the driving frequency of the motor.
The above prior art is directed to solving the problems originating from only one type of vibration mode. However, other types of vibration modes may cause undesirable drive dynamics, e.g., track misregistration and vibro-acoustic disturbances. Elastic vibration of the mount flange and/or the baseplate in a disk drive can cause these types of undesirable drive dynamics.
Yet another problem involves the mounting of the spindle motor and the drive baseplate. Often there are deformities on the baseplate or the motor mount that can affect the stability of the baseplate/mount, which can thereby also contribute to undesirable drive dynamics.
It can be seen that there is a need for a method and apparatus that allows the optimization of the drive dynamics.
It can also be seen that there is a need for a mounting interface between the baseplate and the motor mount that stabilizes the baseplate/mount.
It can also be seen that there is a need for a method and apparatus for dissipating distortion energy emanating from the vibration modes for the disk drive motor.